Bitumen is a petroleum product obtained by the refining of petroleum. Consisting of a high molecular weight mixture of hydrocarbons, bitumen is a dark colored sticky mass with a consistency ranging from springy hard to viscous and with water-repellent properties (see DIN 55 946).
Bitumen is readily worked up at high temperatures owing to its thermoplastic properties.
For most applications, e.g. for the preparation of asphalt mixtures for road construction or bituminous roof coverings, bitumen must be supplied from the refinery in a hot liquid state and kept ready for use in insulated storage tanks.
It is known to prepare a pulverulent bitumen concentrate containing from 10 to 80% by weight of synthetic silica by spraying the liquid bitumen on to silica (German Patent DE-PS 29 33 339) so that the silica is completely covered by bitumen.
The known bitumen concentrate has the disadvantage that, owing to the static pressure, it sticks together during storage and thereby loses its capacity to flow freely. The problem therefore arises of preparing a bitumen granulate which can be stored over a considerable length of time without losing its free flowing property.